1. Field of the Invention
The present invention relates to a manufacturing method of a semiconductor device. A semiconductor device refers to a semiconductor element itself or a device including a semiconductor element. As an example of such a semiconductor element, for example, a transistor can be given. A semiconductor device also refers to a display device such as a liquid crystal display device.
2. Description of the Related Art
In recent years, semiconductor devices have been necessary for human life. Transistors included in such semiconductor devices are manufactured by forming a film over a substrate and processing the film into a desired shape by etching or the like.
In such a manufacturing method of a semiconductor device, for example, a first conductive film is formed, an insulating film is formed to cover the first conductive film, an opening portion overlapping with the first conductive film is formed in the insulating film, and a second conductive film which is connected to the first conductive film through the opening portion may be formed. In such a manner, a plurality of wirings provided using different conductive films is arranged vertically and horizontally; thus an element substrate on which a plurality of elements is arranged in a matrix can be manufactured.
Not only the cross-sectional shape of such an opening portion, but also the state of the surface of the opening portion depends on etching conditions. For example, etching residues exist in the opening portion in many cases. Such an etching residue existing in the opening portion may inhibit a connection of a plurality of conductive films in some cases. As a method for removing such a residue in the opening portion, reverse sputtering can be given (e.g., Patent Document 1).
On the other hand, in recent years, metal oxides having semiconductor characteristics (hereinafter, referred to as oxide semiconductors) have attracted attention. Oxide semiconductors can be applied to transistors (Patent Documents 2 and 3).